One dev cracked open 15 real AI/SaaS products to expose their system prompts
A developer dug through the code of 15 well-known AI and SaaS products to uncover how they write the hidden instructions that control their AI behavior. It's a rare hands-on look at what successful products actually tell their AI behind the scenes.
A system prompt is the secret set of instructions a product feeds to an AI before any user ever types a message — it shapes the AI's tone, limits, and output style. Because these are rarely published, most builders have to guess at best practices. This developer reverse-engineered 15 open or partially open codebases on GitHub to surface the real patterns.
The findings show that well-built products tend to separate role, constraints, and output format clearly in their system prompts, and they spell out edge cases upfront rather than hoping the AI figures it out. For solo developers building or tuning AI-powered tools, this is a concrete, example-driven reference that's hard to find elsewhere.
Key points
- Compares real system prompt patterns from 15 live products side by side
- Well-crafted prompts clearly separate role, constraints, and output format
- Spelling out edge cases in advance is a common trait of successful prompts
- Analysis was done by reading publicly available GitHub repositories
- Directly useful for anyone building or improving an AI-powered product
Quick term guide
- system prompt
- A hidden set of basic instructions that guides how an AI tool behaves.
- reverse-engineered
- Examined finished software backwards to figure out how it was built or what rules it follows.
- codebase
- The full set of files and code that make an app or product work.
- system prompts
- Instructions you give an AI before a conversation starts to shape how it behaves throughout.
- prompts
- Instructions you give to an AI tool.
- edge cases
- Unusual or unexpected inputs that fall outside the normal, expected use of a product.
- developers
- Developers are people who build software, apps, or websites.
- reference
- Using a source to find information or confirm facts while working.